Una aproximación ontosemiótica a la visualización en educación matemática

La visualización es un campo de investigación de creciente importancia en educación matemática. Sin embargo, el estudio de su naturaleza y relación con otras formas de registro y comunicación de información continúa siendo tema de reflexión. En este trabajo proponemos una manera de entender el lenguaje y el pensamiento visual, y sus relaciones con el lenguaje y pensamiento analítico, usando las herramientas teóricas del «enfoque ontosemiótico» del conocimiento matemático. Mostraremos que la noción de «configuración visual» de objetos y procesos, con sus diferentes modalidades contextuales, permite articular diversas perspectivas sobre la visualización, comprender sus relaciones con otras formas analíticas de expresión y reconocer diversos grados de visualización de la actividad matemática

A multidisciplinary study unveils the nature of a Roman ink of the I century AD

A multi-instrumental approach combining highly sensitive Synchrotron Radiation-based techniques was used to provide information on the real composition of a dry black ink powder found in a bronze inkwell of the first century AD. The presence of Pb, Cu and Fe in the powder, revealed by XRF and ICP-OES data, leads to raise several hypotheses on their origin. The inkpot and its lid were also investigated by Hand-Held XRF, revealing a bronze alloy (Cu-Sn) with a certain amount of Fe and Pb. The lid was found to be particularly enriched in lead. XRPD, XAS and FTIR measurements showed a substantial presence of silicates and common clay minerals in the ink along with cerussite and malachite, Pb and Cu bearing-carbonates, respectively. These evidences support the hypothesis of an important contamination of the ink sample by the burial environment (soil) and the presence of degradation products of the bronze inkpot. The combined use of IR, Raman, and GC-MS evidenced that the black ink is mainly composed of amorphous carbon deriving from the combustion of organic material mixed with a natural binding agent, Arabic gum

One-pot RAFT and fast polymersomes assembly: a ‘beeline’ from monomers to drug-loaded nanovectors

Rapid and simple routes to functional polymersomes are increasingly needed to expand their clinical or industrial applications. Here we describe a novel strategy where polymersomes are prepared through an in-line process in just a few hours, starting from simple acrylate or acrylamide monomers. Using Perrier's protocol, well-defined amphiphilic diblock copolymers formed from PEG acrylate (mPEGA480), 2-(acryloyloxy)ethyl-3-chloro-4-hydroxybenzoate (ACH) or 2-(3-chloro-4-hydroxybenzamido)ethyl acrylate (CHB), have been synthesised by RAFT polymerisation in one-pot, pushing the monomer conversion for each block close to completion (≥94%). The reaction mixture, consisting of green biocompatible solvents (ethanol/water) have then been directly utilised to generate well-defined polymersomes, by simple cannulation into water or in a more automated process, by using a bespoke microfluidic device. Terbinafine and cyanocobalamine were used to demonstrate the suitability of the process to incorporate model hydrophobic and hydrophilic drugs, respectively. Vesicles size and morphology were characterised by DLS, TEM, and AFM. In this work we show that materials and experimental conditions can be chosen to allow facile and rapid generation drug-loaded polymersomes, through a suitable in-line process, directly from acrylate or acrylamide monomer building blocks

Valorizzare il Paleolitico. Reti territoriali e buone pratiche.

The Palaeolithic site of Grotta di Fumane, discovered fi fty years ago in the territory of Valpolicella, is an extraordinary testimony to the way of life of Neanderthal Man and the fi rst Anatomically Modern Men thanks to the rich archaeological evidence found in its fi ll. The data collected are crucial for studying the birth of symbolic thought in Homo sapiens and for comparing it with that of Neanderthals. For several years now, the cave has been the object of intense promotion leading to several projects being shared with a wide local network of organizations. The National Archaeological Museum of Verona will soon host two large rooms dedicated to this important Palaeolithic site, equipped with multimedia stations, explanatory panels, casts and thematic showcases

Detecting low-dimensional chaos in time series of finite length generated from discrete parameter processes

One of the truly novel issues in the physics of the last decade is that some time series considered of stochastic origin might in fact be of a particular deterministic type, named "chaotic". Chaotic processes are essentially characterized by a low, rather than very high (as in stochastic processes), number of degrees of freedom. There has been a proliferation of attempts to provide efficient analytical tools to discriminate between chaos and stochasticity, but in most cases their practical utility is limited by the lack of knowledge of their effectiveness in realistic time series, i.e. of finite length and contaminated by noise. The present paper attempts to estimate the practical efficiency of a slightly modified Sugihara and May procedure [G. Sugihara and R.M. May, Nature 344 (1990) 734]. This is applied to synthetic finite time series generated from discrete parameter processes, providing rates of misidentification (obtained through simulations) for the most common stochastic processes (Gaussian, exponential, autoregressive, and periodic) and chaotic maps (logistic, Hénon, biological, Tent, trigonometric, and Ikeda). The procedure consists of comparing with a selected threshold the correlation between actual and predicted values one time step into the future as a function of the embedding dimension E. This procedure allows to infer the presence of low-dimensional chaos even on series of ∼ 50 units, and in presence of a noise level equal to ∼ 10% of the signal amplitude. We apply this method to the sequence of volcanic eruptions of Piton de La Fournaise volcano finding no evidence of low-dimensional chaos. © 1996 Elsevier Science B.V. All rights reserved

Rikitake's geodynamo model analysed in terms of classical time series statistics

Rikitake's geodynamo model is used to generate synthetic series of geomagnetic reversals which are statistically compared with the real series of reversals. The model is found inadequate to represent reality. © 1995

Detecting low-dimensional chaos in geophysical time series

Driven by the great appeal of the potential capability to reduce very complex and highly erratic phenomenologies to simple deterministic and predictable processes, much effort has been devoted to studying chaotic systems. Unfortunately, such studies have been essentially theoretical, and the problem of detecting chaos in real time series has so far received little attention. As a consequence, the available techniques are fairly inefficient and are often misused. Furthermore, if detecting chaos in real-time data would, in any case, be important from a philosophical stand point, only low-dimensional chaos is of practical interest, since it allows an effective short range predictability and could possibly also be modeled. A critical review of the available methods to detect chaos in a real series is presented together with a procedure which is efficient in the presence of experimental errors and with relatively small sets of data. An application to the series of geomagnetic inversions and to the eruptive activity of the Piton de la Fournaise volcano, for which a chaotic dynamics appeared best documented, does not lead to detection of any low-dimensional chaos. Copyright 1997 by the American Geophysical Union

Practical application of fractal analysis: Problems and solutions

Fractal analysis is now common in many disciplines, but its actual application is often affected by methodological errors which can bias the results. These problems are commonly associated with the evaluation of the fractal dimension D and the range of scale invariance R. We show that by applying the most common algorithms for fractal analysis (Walker's Ruler and box counting), it is always possible to obtain a fractal dimension, but this value might be physically meaningless. The chief problem is the number of data points, which is bound to be insufficient when the algorithms are implemented by hand. Further, erroneous application of regression analysis can also lead to incorrect results. To remedy the former point, we have implemented a convenient numerical program for box counting. After discussing the rationale of linear regression and its application to fractal analysis, we present a methodology that can be followed to obtain meaningful results